Telemetering system



' Feb. 24, 1942.

R. G. JEWELL 2,274,415

TELEMETERING SYSTEM Filed Oct. 1, 19.40

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Patented Feb. 24,

, mums 'rnnmz'rsnmo SYSTEM Richard G. Jewell, Lynn, Masa, assignor to General Electric Company, a corporation of New York Application October 1, 1940, Serial No. 359,290 Claims. (Cl. 172-239) My invention relates to a remote indicating system and concerns particularly arrangements for electrically transmitting indications of angular movement. I

It is an object of my invention to provide and a receiver therefor.

A further object of my invention is to provide a' telemetering system which utilizes a small amount of electrical energy. which may be operated on direct current, and which requires only two insulated conductors between the transmitter and receiver, permitting one side of the current source to be grounded.

Other, and further objects and advantages will become apparent as the description proceeds.

In carrying out my invention in its preferred form I provide a transmitter in the form of a potentiometer with a movable tap, and a receiver in the form of an annular core, with a light permanent-magnet rotor and oppositely wound fleld windings on the core. The arrangement is such that the currentin the fleld winding produces a magnetic flux diametrically crossing the core and changing in angular direction with changes of the potentiometer setting. The rotor is caused to take up. a center position when the potentiometer tap is in its middle position and to deflect with shifting of the potentiometer tap to one side or the other.

The invention-will be understood more readily from the following detailed description when considered in connection with the accompany- ..a a compact, reliable, simplified telemetering system pair of insulated conductors i4 and I5 is provided extending between the transmitter II and the receiver II. A third electrically conducting path is required, which may take the form either of a conductor it which need not be insulated or may be formed by the metallic framework of the structure on which the telemetering system is mounted. In this latter case suitable terminals of the transmitter ll, receiver l2, and the current source i3 would be grounded to such framework. The current source B may be located either at the transmitting station II, at

the receiving station I! or at some other point, r

as found most convenient in any particular in-- stallation.

The telemetering apparatus illustrated is not limited in its usefulness to any particular class of service, but owing to its lightness, compactness and low energy requirements, it is well adapted to use on aircraft for transmission of instrument measurements and the indications of angular positions. One of the applications forwhich it is adapted, for example, is the remote indication of the position of landing gear for which dials may be used, such as illustrated in Patent 2,l81,803-l aus-Remote indicator, and Design Patent ll2,743Haven-Design for an airplane landing indicator. Other applications are for transmitting to the cockpit of the airplane, measurements of engine speed and en- 'gine temperature. fuel quantity, and the like.

' The particular forms .of pointers, dials, and

ing drawing and those features of the invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. In the drawing. Fig. l is a circuit diagram schematically representing one embodiment of my invention showing the position of theapparatus with the pointers at the transmitting and receiving ends in the center position. Fig. 2 is a diagram of the apparatus of Fig. 1 showing the condition with the pointers at one extreme end of their scales, Fig. 3 is a schematic diagram of a modified form of receiver for the system shown in Figs. 1 and 2, and Fig. 4 is a view of a section through the core cut by a plane 4-1. Like reference characters are utilized throughout the drawing to designate like parts.

In the drawing, the transmitter is designated as a whole by the reference numeral II and the receiver is designated as a whole by the reference numeral II. A source of direct current It is employed for energizing the apparatus, and a scales employed are not a part of my present in vention and suchparts of the apparatus are, therefore, not shown in the drawing, which illustrates only the internal mechanism of the transmitter and receiver.

The transmitter is in the form of a rheostat or potentiometer consisting of a resistor H and an adjustable tap therefor It. The resistor Il may be either straight or' curved according to whether the indicator at the transmitting station moves along astraight line or angularly, but for the sake of illustration a resistor i1 is shown which is shaped-in the form of an arc of a circle, or which may have contacts arranged on the arc of the circle. The embodiment of the invention represented in the drawing is a system for transmitting an angular indication over a degree scale from a transmitting point to a receiving point. Accordingly, the resistance H has an arc of120 degrees. .The transmitter II has three terminals. There are terminals i9 and 2| at the ends of the resistor l1 and one of these terminals, for example, the latter may rotation at the center of the arc of the resistor IT. The terminal I! is connected to the insulated conductor I5 and the terminal 2| is connected to the insulated conductor H. The

current source l3, which may be a battery of dry or storage cells, has a pair of terminals 23 and 24, one of which may be grounded. In the arrangement illustrated, the terminal 24 is a negative terminal and is grounded. The positive terminal 23 of the current source I3 is connected to the insulated conductor l5 leading from the. ungrounded end of the transmitterresistor I1.

The receiver I2 comprises a rotor 25 and'a stator, comprising an annular core 26 carrying a pair of stator or field windings 21 and 28.

The rotor 25 is composed of high-coerciveforce permanent-magnet material and is magnetized transversely to the axis of rotation, is preferably mounted concentric with the annular stator core 25, and has a circular cross section, being cylindrical in the apparatus represented by the illustrative drawing. The polarity of the permanent magnet rotor is represented by the letters N and S and the direction of the magnetic field produced by the rotor magnetization is represented by an arrow 29-. For reasons which will be explained hereinafter, it is preferable to arrange the design in such a manner that the line of magnetization is substantially as shown in Fig. 1 when the pointer or dial carried by the rotor is approximately in the middle of its scale range in the case of uniform scale distribution. According to the type of indicator or instrument to be employed, a suitable pointer, target or dial is secured to the rotor 25 and it is represented in the drawing by a fragmentary pointer 30, the apparatus being so arranged for the sake of convenience in explanation that the pointer 30 of the receiver and the arm 22 of the transmitter have the same angular position.

For the sake of lightness, high torque and high damping, the rotor 25 is preferably composed of a material having relatively low density, but high coercive force, and a strong tendency to retain precisely a given line of magnetization. For example, sintered oxide may be employed composed of magnetite, ferric oxide and cobaltic oxide, substantially in the 30.1% ferric oxide and 26.3% cobaltic oxide, respectively, such as that described in the patent gfl G. Arey and Harold T. Faus, Number proportions of 43.6% magnetite,

granted December '7, i937, and assigned to the same assignee as the present invention. When composed of this material, the rotor consists of a solid unlaminated block of circular cross section which is polarized across a diameter thereof. The material is prepared and magnetized as follows:

Mixtogether finely powdered magnetite, ferric oxide and cobaltic oxide in the proportions of 43.6% magnetite, 30.1% ferric oxide, and 26.3% of cobaltic oxide. Mold the mixture in the shape desired under pressure of from three to five tons per square inch; Remove from mold and heat in an atmosphere of nitrogen or air for two or three hours at about 1000 degrees C.and allowto cool. Then rehetitgabout 520 degrees C. in a special furnace placed-in the air gap of a direct-current V electromagnet withafield of-about 3000 H. With the field on, lower' the. temperature to about 300 or 320 degrees C. and hold in the field within this range of temperature for about threequarters of an hour. Then allow to cool in the field to below 100 degrees C. The material may then be machined or ground to shape, if neces sary. An unusual property of this material which I have discovered and which makes it particularly suitable for telemetric receiving is that although it may be magnetized in a given transverse direction while hot it is virtually impossible thereafter to shift the line of magnetization to a diilerent angle without raising the temperature to about 300 degrees. It is believed that the materials described in United States Patents No. 1,097,193 and No. 1,976,230 to Kato et a1. will also be useful for the rotor material on some forms of the apparatus although I have found that the sintered oxide material which I have described, produces telemeter receivers with the best performance.

Such material after being magnetized, in addition to being a permanent-magnet of exceptionally high coercive force and adequate, although lower, residual induction than some of the common permanent magnet materials, has other remarkable properties. It has a resistance between 600,000 and 1,000,000 ohms per cm. cube and is thus practically an insulator. It is hard,

and of a gray slate color. It is very light in weight as compared to other magnetic materials, having a specific gravity of approximately onehalf that of ordinary steel. The coercive force of the material prepared as previously described is between 700 and 1000 oersteds and the residual induction is about 2000 lines per square centimeter. The available magnetic energy of the material per unit volume is approximately 1,000,000 measured in terms of the maximum value of the product of flux density and field strength in lines per square centimeter or Gausses and in Gilberts per centimeter respectively. Accordingly, the ratio of the magnetic energy per unit volume to the specific gravity or the magnetic energy per unit mass is over 2,000,000

; measuring specific gravity in terms of that of steel. Likewise the ratio of residual induction to specific gravity exceeds 4000.

Since the line of polarization is very definite and fixed and does not shift, the scale need not be recalibrated and reset in case the windings should be deenergized and reenergized with the rotor in a different position. As a cylindrical magnet composed of the sintered oxide material behaves Just as if it were a thin line permanent magnet, the position assumed by the pointer is very definite and the exact position may be relied upon as an accurate indication of the measurement transmitted.

The core 20 may be in the form of an annulus having a rectangular cross section, as shown in Fig. 4', but the particular shape of cross section is not essential to carryout the invention. It is desirable, however, to provide an air gap 3| in the annulus along the diameter along which the direction of rotor magnetization 29 lies when the rotatable pointer II is substantially in the middle of its scale range in the case of a uniformly calishielding with low losses, the core 20 is preferin series between a pair oi stator'termlnals 22- and 22, one of which, for example, the latter, may be' grounded. The Junction point of the windings-21 and 2| is brought out to iorm a third terminal 24. The terminals 22, 32 and 24 serve as the receiver terminals. One stator coil is connected oppositely with respect to the other so that current in flowing from terminal 32 to terminal 23 produces a polarity oi the coil 21 tending to cause flux to pass circularly in the opposite direction to the flux produced in the core 2' by the polarity oi the coil 2|. The ungrounded end receiver terminal 22 is connected to the conductor I! to which the ungrounded side of the current source I! is connected, and the coil junction terminal 24 oi the receiver I2 is 1 system will most readily be understood by first considering the parts in the position shown in Fig. 1. It will be apparent that an electrical circuit is iormed from the positive terminal 22 oi the battery ll, through the conductor l8, coil 21, the coil 28, back through the ground II, to the negative. terminal 20 of the current source II. There is likewise a parallel circuit irom the positiveterminal 22 through the conductor IS, the resistor I1 and ground to the grounded terminal 24 of the current source l1. The conductor 14 has no effect on the circuit since it is connected between the middle point on the resistor II to the junction terminal 24 oi the receiver i2, it being understood that for uniform or symmetrical scale calibration the coils 21 and 28 are identical, with the same resistance.

Accordingly, the opposing fluxes produced by the coils 21 and 28 in the core 26 meet at the ends of the vertical diameter of the core 28 and pass downward diametrically from the upper point on the annulus toward the air gap 2|, as

shown by the flux lines 35. With'the connections shown, the upper point of the annulus has north polarity and the point adjacent the air gap has south polarity so that the rotor 25 takes the position indicated with the south pole at the top and the north pole at the bottom, and the line of magnetization 29 vertical.

It the indicating arm 22 oi the transmitter II is shiited in one direction or the other, the symmetry oi the electrical circuit is upset and one or the other of the coils of the receiver is partially short circuited. Looked at another way,

- the relative values of two series voltages applied age and becomes dead so that all the flux acting [in the receiver is produced by the coil 2.. Owing to the iact that the air gap 2| produces some reluctance in the iron circuit oi the core 2|, an appreciable leakage flux crosses the central opening of the annulus 22, as illustrated by the flux lines 25' in Fig. 2. The flux path at the center oi the annulus is along a diagonal diameter the ends of which are half way between the coil 2| and air gap II. It will be understood that the duo! the air gap 2| is made such,

. in relation to the inside diameter oi the annulus 26 and the magnetic properties of the core material, that the diametral flux is substantially oi the same strength as in the condition oi Fig. l. The coils 21 and 22 are so mounted in the specific embodiment illustrated that their centers are spaced approximately degrees,'and symmetrical with respect to the vertical diameter oi the annulus 20. Consequently, the direction oi the flux crossing the center oi the annulus 28 is substantially along a line, 60 degrees irom the vertical, upward to the left, when the coil 21 is short circuited. Accordingly, the rotor 25 is deflected 60 degrees with its line oi magnetization 28 following the flux lines in the center oi the annulus 26. Consequently, the rotor pointer 30 is shiited to the left 60 degrees, taking up the position shown in Fig. 2. It will be understood that intermediate positions between center and extreme left will be taken up by the pointer 30 when the transmitterindicator arm 22 is moved to positions between extreme left and the center position, and likewise the corresponding positions to the right are taken up when the arm 22 is shifted to the right oi center.

It will be understood that the best dimensions and mechanical and electrical relationships for .the various parts of the system will depend upon the type of service to which the telemetering system is to be applied, My invention obviously is not limited to any particular numerical values. However, I have found that in instruments for use on aircrait, very satisfactory results are obtained in which specific values are approximately ence oi the current source II, 10-15 volts D. C.;

coils 21 and 2!, about 530 ohms,'each with 2,000 turns and a combined energy consumption oi about ya watt when the rotor is in the center position; resistor l1, total resistance about 200 ohms, energy consumption of about 1 watt.

Owing to the high magnetic energy and residual magnetization oi the sintered oxide rotor. a minimum flux density of 250 Gausses, due to the rotor, is maintained in the space between the rotor and the annular core 2|. Consequently, a relatively small magnetomotive iorce need be supplied by the stator. In other words, ver small field current sufiices. Owing to the fact that the greater mangetomotive iorce is produced by the rotor, a strong positive damping action may be provided, ii desired, as well as high torque.

Damping may be produced by providing a damping cup 2!, as illustrated in Fig. 3, the cup being composed of a suitable, highly conductive material, such as copper. It will be understood, however, that a certain amount of damping is provided by the fact that the circuits of the coils 21 and 28 are closed through the resistance II. It will be observed that the flux produced by the stator, that is, by the field windings 21 and 28, is primarily for the purpose of directing the rotor, and that the greater portion of the magnetic energy is provided by the rotor flux. In this way, -a light, compact, low-loss system may be provided for aircraft in which weight is at a premium and it is highly desirable to utilize a system having current conducting windings which carry but little current and consequently have ,relatively little heat loss, in order that fine wire and compact units may be employed without danger of overheating.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principl and showing its application but it will be obvious'to those skilled in the art that many modifications and variations are possible and I aim, therefore, to cover all such modifications and variations as fall within the scope of my invention which is defined in the appended claims. 1

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A telemetering system comprising a source of direct current, one side of which" may be grounded, a transmitter, a receiver, and a pair of conductors, the transmitter comprising a resistor ounded at one end with a teminal at the other end and a tap movable in response to indications to be transmitted, said terminal and said tap respectively connected to the first and second of said conductors, said current source being grounded on one side and having its ungrounded side connected to the first of said conductors, said receiver comprising an annular core of magnetizable material, a transversely magnetized permanent magnet rotor rotatably mounted within said annular core substantially concentric therewith, and a pair of windings linking s'aid core, said windings being connected in series opposition with respect to flux flow circularly through the core and having a junction point connected to the second of said conductors, the first of said conductors being connected to the fre end of one of said windings, the free end of the other of said windings being grounded, whereby said resistor shunts the current source and the series connected windings, and adjustment of the tap on said resistor varies the relative strength of the currents flowing in said windings to cause variation in angular direction of the fiux produced by the stator windings dia with the relative voltages existing across the said I coils, whereby the angular position of the rotor may be varied.

3. A receiver for a telemetering system comprising an annular core of magnetizable material and a permanent magnet rotor mounted rotatably with respect to an axissubstantially concentric with said core, said stator core carrying a pair of electrical coils connected in opposition and adapted to have voltages applied thereto adjustable in ratio, said coils being mounted on diflerent portions of the annular core with the center portions of the coils less than 180 degrees apart on the annular core, whereby the currents caused to flow in said cells by said applied voltages produce magnetomotlve forces acting in opposition circularl in the annular core to cause magnetic flux to cross the annular core diametrically, the angular direction or the magnetic flux at the center of the annulus varying in accordance with the relative strengths oi currents in said coils to cause deflection of the permanent magnet rotor in accordance with the variation metrically crossing the stator core, thus in turn,

determining the angular position of the rotor.

2. A receiver for a direct-current telemetering system of the type including means for transmitting to a receiver a pair of series connected voltages adjustable in relative magnitude, said receiver comprising an annular core with an air gap therein, a pair of windings linking said core, and a rotor substantially concentrically mounted within said core and magnetized transversely to its axis of rotation and the axis of the annular core, said windings being connected in series opposition with respect to flux flowing circularly within the core, said coils having end terminals and a junction serving as a mid terminal, whereby the series connected transmitted voltages of th -telemetering system may be applied to said.

coils respectively, the length of the air gap in the core being such that leakage flux passing diametiically across the stator core suffers no excessive variation in magnitude with variation in relative magnitude or said voltages, the angular direction a: mid diametrical flux chanilnfl in accordance in the relative strengths of voltages applied to said coils.

A receiver for a direct-current telemetering system of the type including means for transmitting to a receiver a pair of series connected voltages adjustable in relative magnitude, said receiver comprising an annular core, a pair. of windings linking said core, and a rotor substantially concentrically mounted within said core and magnetized transversely to its axis of rotation and the axis of the annular core, said windings being connected in series opposition with respect to flux flowing circularly within the core, said'ooils having end terminals and a junction serving as a mid terminal, whereby the series connected transmitted voltages of the telemetering system may be applied to said coils respectively, the angular direction of said diametrical flux changing in accordance with the relative voltages existing across the said coils, whereby the angular position of the rotor responds to. the relative magnitude of said voltages.

5. A receiver for a direct-current telemetering system of the type including means for transmitting to a receiver a pair of series connected voltages adjustable in relative magnitude, said receiver comprising substantially annular magnetic core means, a pair of electrical windings linking said core means, a rotor mounted between said windings substantially concentric with the core means, said'windings being connected in series opposition with respect to a magnetic circuit including both of them, and being mounted with their magnetic axes at an angle to each other,

said magnetic core means including a portion providing a sufiiciently low reluctance path between said windings to cause leakage flux to travel in said path between said windings diametrically across the core and to intersect said rotor, said coils having end terminals and a junction serving as a mid terminal, whereby the series connected transmitted voltages of the telemeterin; system may be applied to said coils respectively, the angular direction of said leakage flux changing in accordance with the relative voltages existing across said coils, whereby the angular position of the rotor responds to the relative magnitudes of said voltages, the length and reluctance of the diametrical fiux path being substantially the same tor various angles owing to the annular shape of the core means.

- RICHARD G. JEWELL. 

